deck extention support problem

ron shewchuk

I will be extending a deck that is attached to the house. Existing deck is 12x16. Attached to the house on the 16'side. Deck has been there for 12 years, is in perfect condition and gets lots of use.
It is supported, 12' out from the house on 2 4"x4" posts 12' high and sitting on concrete post pads directly on the ground. The post pads have never moved.
We live in north/central Quebec, Canada and have frost down to about 3 feet.
Everything I read say's not to use concrete post pads but to put in concrete filled Sono tubes. extended below the frost level.
If I do this I will have one inserted concrete post and 2 "floating" posts on post pads.
Can I use another Concrete Post pad to support the extension, since this has been perfect for 12 years. Can I use one concrete dug down post support and 2 floating pads, which seems like it would cause some variable movement issues in the spring, or do I need to replace the two existing post bases and replace them with concrete filled Sono tubes inserted down below frost level?
Ron

Daniel Holzman

Not really sure I understand exactly what you are planning to do. Let's assume you are building an addition on to the existing deck, perhaps that is what you mean by the word extension. I am guessing from your location description there are no codes to guide you.

You could certainly build the "extension" as a completely separate, supported deck, with new footings and posts. You could then connect the perimeter beam from the extension to the perimeter beam from the original deck. There are several other options, however without photos and a plan I can't really grasp your idea.

Where I live, code requires that posts be supported on concrete footers (usually sonotubes) that extend below frost. The posts are connected to the concrete post using galvanized stand off brackets (Simpson makes a variety of different ones). Also the posts are required to be a minimum of 6x6 inches, PT. However, your code (if you have one) may require different techniques. Also, Massachusetts frost depth is typically taken as 4 feet, I am a bit surprised you are at only 3 feet up in Quebec.

12penny

I'll be the second to ask for pictures, please.

My thoughts...yes, you should have all posts on foundations set below the frost line.

There's more but I'll wait for pics.

robertcdf

Pictures and plans would make this so much easier...

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12penny

Offline...may be a little while.

woodworkbykirk

based on what you have now i would most definitely replace the concrete pads with footing peirs. not only that current codes wont allow you to have 4x4 posts for supporting your deck they must be 6x6.. the fact its 12' up worries me with the deck sitting on pads and not piers they can move that much more and could structurally fail.

if you replace the existing 4x4's with 6x6's you can create a 2 tier deck.. keep the existing portion at its current height then have the addition step down by letting in a new beam into the 6x6's then take the deck out from there

ron shewchuk

Hi thanks, I will at least, build the deck extension as a properly supported completely separate entity and join together as suggested. The project is country house we won't get to until end March. I'm in planning stage now. I'll certainly post photos when we get there, before we start on the deck.
I'll check local codes as well. I appreciate your clear concise response.

joecaption

The deck you have now would never pass inspection in my area.
Must be 6 X 6's for that height.
And to only have two post for that long a span I would have to have 2 X 10's min. for ledger and floor joist.